M. P. Tombs, Plant Physiology, 42, 797 (1967) describes a method of isolating protein bodies from soy meal by density gradient centrifugation using a 70% to 90% (wt/vol) aqueous sucrose solution having a density from 1.25 to about 1.34. The reference also describes the swelling and bursting of protein bodies when the meal is placed in contact with water, a problem which is said to be solved by buffering at pH 5.
Certain other density fractionation-type processes for separating protein from other cellular materials are known. U.S. Pat. No. 3,828,017, Finley, et al. (1974) discloses the centrifugation of a slurry of pulverized soy material and liquid fluorocarbon having a density of 1.35 to 1.45.
Other methods for isolating protein have involved extraction with mixtures of polar and nonpolar solvents and dissolution with reprecipitation of protein. U.S. Pat. No. 2,278,670, Rauer, Apr. 7, 1942, discloses a two-step process for recovering protein using organic solvents and alkali.
U.S. Pat. No. 3,043,826, Beaber, et al., July 10, 1962 discloses the extraction of protein from alcohol-treated soybean material by contact with water at alkaline or acidic pH's and with subsequent recovery by precipitation.
Japanese Pat. No. 2,130,942, Ajinomoto, Apr. 22, 1976 (abstract) discloses the separation of protein material by isoelectric precipitation.
Other separation procedures are also known. U.S. Pat. No. 3,734,901, Hayes, et al., May 22, 1973 discloses a protein concentration step in which nonproteinaceous materials are separated from vegetable seed material using a monohydric alcohol/water extraction medium. U.S. Pat. No. 3,649,293, Hoer, et al., Mar. 14, 1972 teaches the separation of protein by solubilizing the protein, depositing the protein on solid cellular material, and separating the protein-carrying solids, which are processed further.
Claim 1 of U.S. Pat. No. 4,089,848, Bell, et al., May 16, 1978, discloses a method for separating protein from de-oiled oats. The claimed process involves dissolving oats in alkaline solution, acidifying to separate acid soluble impurities, and then recovering acid soluble protein.